This invention relates to the pipeline industry where steel pipe is lined with a thermoplastic liner (such as, but not limited to, polyethylene, nylon and other polyolefins) to prevent internal corrosion, and in some cases (Roach, U.S. Pat. No. 115,072,622 dated Dec. 17, 1991) the liner is used to monitor the integrity of the steel host pipe.
There are basically two types of liners that are presently installed: (A) tight-fitting liners, where the outside diameter of the liner is installed insitu against the inside diameter of the host pipe, and (B) loose-fitting liners, which are installed with a space between the inside diameter of the host pipe and the outside diameter of the liner. After installation, the internal working pressure of the host pipe, heat, and/or other methods cause the liner to expand against the inside diameter of the host pipe; for example, steel line pipe used in the pipe line industry to transport refined liquids and natural gas over long distances.
This Pressurized Dies invention specifically addresses the method of reducing a liner that has an outside diameter which is approximately 5% larger than the inside diameter of the host pipe so it can be installed insitu. The liner, after being reduced and installed, will increase in diameter spontaneously, without the aid of (A) heat, (B) internal pressure of the host pipe, (C) reforming a liner that has been extruded in shapes smaller than the host pipe's inside diameter, or (D) other methods.
The basic technology of installing liners "against the wall" involves (1) the reduction of a plastic liner, not exceeding its elastic limits in the axial direction and pulling the liner into the host pipe, and (2) not exceeding the plastic liner's elastic limits in the longitudinal direction. After the plastic liner is installed, it is allowed, over time, to relax and expand to its original size. However, the plastic liner will be prevented from expanding to its original size, and will instead press against the inside diameter of the host pipe; therefor resulting in an interference fit and remain tight against the host pipe's inside diameter.
As the host pipes become larger in diameter (12" plus), or a particular construction job involves several different sizes of liners, it becomes very expensive to build reduction machines that may, for example, involve roller reduction machines, as each size requires a specially-made set of rollers. These increased costs are normally passed on to the client.
In the case of the technologies using reduction dies, with or without heat, etc., there exists a major problem of the liner being over-stressed and exceeding their elastic limits in the longitudinal direction due to the friction, or drag, as they are pulled through the dies.
The Pressurized Dies invention will allow the liner pipe to pass through the reducing dies with less friction and drag. This further allows the liner pipe to be pulled into the host pipe and requires less connections between "pulls". Fewer connections and longer "pulls" result in less cost to the contractor and the client. Consequently, the Pressurized Dies invention is a more cost-effective system than other systems known to the art.
To change the size of the dies is inexpensive, as compared to "roller" alternatives and other systems. This also translates into reduced costs to the client, as it is expensive to dig out the existing pipelines in short lengths to install short "pulls" of liners.
The Pressurized Die invention is novel in its approach to liner reduction and is cost effective to the client as related to utility.